After loads of research I decided this swivel is the one. It's more expensive than the competition, but more solid. The safe has a better lock, the swivel is smooth, the fitting was simple, there is no noisy rattle when driving and in my opinion it looks like a more factory-esque fit than the cheaper swivels.

To turn the seat around is pretty easy, but you do need to slide the seat forward for the first 90 degrees, then back a little to get it past the handbrake. If it's raining outside, it can be done with the door closed while your sat in the seat - just.